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Is the expanding bull's-eye effect leading to greater and more frequent weather disasters?

Despite decades of improvement in activities aimed at reducing impacts from extreme events, the rapid increase in disaster losses and people affected suggests that swelling populations, development trends, and vulnerabilities are outpacing mitigation, leading to greater event frequencies and amplified impacts. Due to data, computational, and methodological restrictions, research quantifying changes in human exposure to hazards has been relatively limited. Our research attempts to rectify this deficiency, advancing a framework for future work exploring how exposure and vulnerability contribute to disasters.

Our investigation employs historical exposure data on a uniform grid to appraise how transformations in Chicago's land use have led to greater potential for tornado disasters. Chicago is an ideal example of the enormous growth that metropolitan regions have witnessed during the last century. The area is characterized by a dense urban core and has experienced extensive, spatially fragmented suburban growth, or sprawl. We argue that this development pattern leads to an "expanding bull's-eye effect"--that is, people, their possessions, and infrastructure are increasingly exposed to geophysical hazards as populations grow and spread. Accordingly, it is not solely the population magnitude that is important in creating disaster potential; it is how the population is distributed across the landscape that determines how the underlying disaster components of risk and vulnerability are realized.

We couple synthetic tornado events and event-derived (Joplin, Missouri EF5) damage context with a spatial modeling approach to evaluate the expanding bull's-eye effect using the superposition of hypothetical tornado events atop varying development morphologies. Results show that the number of people and their housing continue to geographically expand, confirming that more people and their possessions are potential targets for tornadoes. We illustrate how differing development types lead to varying exposure rates that contribute to the unevenness of potential weather-related disasters across the region. For instance, a sprawl type of suburban development has led to the greatest change in hazard exposure setting. Conversely, while population loss along the periphery of the urban core has decreased the number of people potentially affected, those that remain may be highly vulnerable due to enhanced sensitivity/susceptibility and reduced adaptive capacity caused by poverty. More recently, inward migration to the central business district has promoted a very dense exposure in the urban core with concentrated catastrophic disaster potential that could potentially overwhelm critical infrastructure.

While climate change may amplify the risk of certain hazards, the root cause of escalating disasters is not necessarily event frequency, or risk, related. Rather, our research confirms that the upward trend in disasters is predicated on increasing exposure and vulnerability of populations.

We recommend a worst-case hazard scenario approach using representative hazard models on high spatial resolution datasets of vulnerability as the basis for mitigation planning and action. Communities need to understand how local exposure landscapes have transformed spatiotemporally and how those changes may influence the tasks of warning, rescue, and recovery should a catastrophic scenario come to fruition.--Walker S. Ashley (Northern Illinois University), S. Strader, T. Rosen-Crants, and A. Krmenec. "Spatiotemporal Changes in Tornado Hazard Exposure: The Case Of the Expanding Bull's Eye Effect in Chicago, IL," in a forthcoming issue of Weather, Climate, and Society.
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Title Annotation:PAPERS OF NOTE
Author:Ashley, Walker S.
Publication:Bulletin of the American Meteorological Society
Geographic Code:1USA
Date:Apr 1, 2014
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